Current DLCO simulators require large and expensive dual-syringe devices. For example, the Hans Rudolph DLCO simulator, as described in U.S. Pat. No. 6,415,642 requires two syringes (3 and 5 liters) that are joined by a manifold via a three-way valve. The manifold is connected to the DLCO equipment. Prior to the start of the simulation test, the 3-liter syringe is filled with a precision gas mixture emulating typical alveolar gas concentration seen in patients. Using the three-way valve, the 5-liter is connected to the DLCO equipment while the 3-liter syringe is isolated with the prefilled precision gas mixture. During the inhalation phase of the DLCO test maneuver, the 5 liter syringe simulates tidal breathing, exhalation to residual volume, and rapid inhalation to TLC. During the breath hold period, the 3-way valve is turned redirecting the DLCO device to the 3 liter syringe. After the breath hold, the content of the 3-liter syringe is emptied into the DLCO device.
The Hans Rudolph simulator “establishes” approximate target DLCO values for the DLCO device under test by controlling the inspired volume as well as the inspired and alveolar gas concentrations. To verify equipment performance over its specified range of operation, it requires multiple precision alveolar gas mixtures with different concentrations of CO and tracer gases.
Because the Hans Rudolph does not control the breath hold time, the breath hold time reported by the DLCO device under test is required to confirm the exact target value. Hans Rudolph provides software for the calculation of the exact target value (based on Eq (1)) after the test is performed.
For trouble-shooting, ATS-ERS (MacIntyre N. et. al. Standardization of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J 2005; 26: 720-735) also recommends the following:                1. Leak testing if it is appropriate to the device under test        2. A DLCO test with a calibrated 3.0-L syringe should be used, which is performed by attaching the syringe to the instrument in the test mode. Test gas is withdrawn from the DLCO machine by the syringe and then reinserted at the end of the breath-hold. The measured DLCO should be near zero and the measured VI should be ≈3.3 L (3.0 L×the body temperature, ambient pressure, saturated with water vapor (BTPS) factor). This procedure checks the inhaled volume accuracy in the DLCO test mode, which may be in error when spirometry measurements are not.        
The simulator identified in the ATS-ERS DLCO testing guideline (MacIntyre N. et. al. Standardization of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J 2005; 26: 720-735) was developed by Glissmeyer, et. al. (Glissmeyer E W, Jensen R L, Crapo R O, Greenway L W. Initial Testing with a carbon monoxide diffusing capacity simulator. J Invest Med 1999; 47: 37A) and manufactured by Hans Rudolph, Inc, Kansas City, Mo.
Current DLCO testing devices and practices suffer from several deficiencies and disadvantages. The trouble-shooting methodology suggested by ATS-ERS (using a 3 liter syringe) does not affirm the DLCO measurement accuracy of a DLCO device over its intended range of operation. At best, this test establishes the accuracy of flow/volume measurement component of the DLCO device. It may also demonstrate that the CO and tracer gas detectors have similar response (but not necessarily accurate or linear) over a narrow range of gas concentrations.
The use of the Hans Rudolph simulator for quality control of DLCO measurements has been well documented (Jensen R, et. al. Quality control of DLCO instruments in global clinical trials. Eur Respir J 2009; 33: 1-7. Jensen R L, et. al. Instrument Accuracy and Reproducibility in Measurements of Pulmonary Function. Chest 2007; 132: 388-395.).
There are a number of challenges and disadvantages in using the Hans Rudolph simulator. First, the procedure is complex and prone to errors. The 3-liter syringe used to simulate exhalation must be filled with precisely known concentration of alveolar gas prior to each test. The syringe must be adequately purged prior to filling. Difficulties arise from a significant certainty that the syringe is properly purged of any previously used gas mixtures. Moreover, during the testing process, the 3-way valve must be turned immediately before the emptying of the 3-liter syringe begins to ensure any chance that the test is accurate. If precise timing of the operation of the 3-liter syringe is not maintained the test of the DLCO equipment is invalid and the test must be re-performed, resulting in increased costs for the precise gas mixtures used in the testing or even improper calibration of the DLCO equipment based on faulty test results.
Second, target DLCO value changes with every test and every new gas cylinder. To ensure that DLCO device operates correctly throughout its intended range of operation, it must be tested at various combinations of CO and tracer gas concentrations, thereby requiring a number of precision (typically 1% or better) pre-mixed gases. Switching alveolar gas bottles adds to the complexity and cumbersomeness of simulator testing.
Third, precision gases are expensive. Delivery and shipment of the precision gases are difficult as these gases are typically classified as medical gases by many countries. One purpose of DLCO equipment is to perform clinical studies or trials in remote locations. For studies and trials to have statistically valid results, the DLCO equipment, which may be in multiple remote locations, must be properly calibrated. This calibration of multiple, remote DLCO equipment simulators is complex in and of itself and even more so with the added cost and complexity of shipping the required medical gases used in the testing.
Fourth, the current DLCO simulators, even though a fraction of the cost of the DLCO device, is relatively expensive. Current simulators require their own test gas which can be costly
Fifth, current simulators are bulky, which also adds to their cost. They require two syringes along with precision test gases. As discussed above, shipping and other costs for current simulators are high not only because of the required precision gases, but costs can increase for storage of the simulator and the gases it requires. All of these costs are exacerbated considering that many times DLCO equipment is used in remote and often poor locations and for non-profit endeavors, such as clinical studies or trials.
Although present devices are functional, they are not sufficiently accurate or otherwise satisfactory. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.